The present disclosure relates to wind turbines, particularly shrouded wind turbines that can be used for mounting additional devices upon the shroud. In particular, advertising displays or surfaces and solar panels are contemplated to be mounted.
Conventional horizontal axis wind turbines (HAWTs) wind turbines have three blades and are oriented or pointed into the wind by computer controlled motors. These turbines typically require a supporting tower ranging from 60 to 90 meters (200-300 feet) in height. The blades generally rotate at a rotational speed of about 10 to 22 rpm, with tip speeds reaching over 200 mph. A gear box is commonly used to step up the speed to drive the generator, although some designs may directly drive an annular electric generator. Some turbines operate at a constant speed. However, more energy can be collected by using a variable speed turbine and a solid state power converter to interface the turbine with the generator. Although HAWTs have achieved widespread usage, their efficiency is not optimized. In particular, they will not exceed 59.3% efficiency, i.e., the Betz limit, in capturing the potential energy of the wind passing through it.
Several problems are associated with HAWTs in both construction and operation. The tall towers and long blades are difficult to transport. Massive tower construction is required to support the heavy blades, gearbox, and generator. Very tall and expensive cranes and skilled operators are needed for installation. In operation, HAWTs require an additional yaw control mechanism to turn the blades toward the wind. HAWTs typically have a high angle of attack on their airfoils that do not lend themselves to variable changes in wind flow. HAWTs are difficult to operate in near ground, turbulent winds. Furthermore, ice build-up on the nacelle and the blades can cause power reduction and safety issues. Tall HAWTs may affect airport radar. Their height also makes them obtrusively visible across large areas, disrupting the appearance of the landscape, which may be objectionable. Finally, downwind variants suffer from fatigue and structural failure caused by turbulence.
The blade of a HAWT typically has an airfoil shape that creates a lower pressure behind the blade as the blade passes through the air. This lower pressure creates a suction effect that follows the blade and creates a large wake to form behind the HAWT. This wake can reduce the amount of power captured by wind turbines downstream of the wind turbine creating the wake by up to 30%. To reduce the amount of power depletion, downstream turbines are often offset laterally from the upstream turbine, and are placed about 10 rotor diameters downstream of the upstream turbine as well. This displacement requires a large amount of land for a wind farm, where several wind turbines are placed in a single location.
The various components of the HAWT, such as the gearbox, the rotor shaft, generator, pitch and yaw controls, and brakes, are generally located within the nacelle of the HAWT. The nacelle may have dimensions such as 24 meters in length by 6 meters in height by 6 meters in width (˜79 ft long×20 ft high×20 ft wide). The nacelle usually weighs at least 10 tons, and can weigh as much as 60 tons. The nacelle itself is usually made from two pieces, a bottom and a top. The bottom piece of the nacelle is anchored to the tower, the various components are placed inside the bottom piece, and the nacelle is completed by placing the top piece to cover all of the various components. The resulting outer surface of the nacelle is generally not smooth, flat, or even. In addition, the outer surface can be difficult to see or look at due to the movement of the conspicuously visible HAWT blades.
Modern HAWTs, while having a large area swept by their blades, typically have a low solidity (blade surface area divided by total swept area) of about 7%. In many cases, large HAWT wind farms are also located in very sunny areas that could be used to capture solar energy. However, the low surface area of a HAWT does not allow for efficient capture of solar energy. In addition, the footprint of an individual HAWT on the land can be rather large, and may preclude other uses of the land, for example due to safety issues from flying ice or blades breaking.